From the most distant stars in the sky to the screen in front of your face, light is everywhere. But the exact nature of light, and how it travels, has long puzzled scientists. One question in particular has vexed thinkers from Issac Newton to Albert Einstein: Is light a particle or a wave?
"Whether light is a particle or a wave is a very old question," Riccardo Sapienza, a physicist at Imperial College London, told Live Science. As a species, we seem driven to understand the fundamental nature of the world around us, and this particular puzzle kept 19th-century scientists busy.
